As a magnetic recording medium (hereinafter referred to merely as "magnetic tape" in some cases) for audio recording, video recording, or for computers, generally a magnetic recording medium (e.g., in the form of a tape or disk) comprising a non-magnetic support having coated thereon a magnetic layer having dispersed in a binder ferromagnetic particles consisting of acicular crystals such as .gamma.-Fe.sub.2 O.sub.3, Co-containing magnetic iron oxide, and CrO.sub.2 has been used.
However, with the recent increased demand for high density recording in a magnetic recording medium, hexagonal crystallized ferrite particles such as substitution products of barium ferrite, strontium ferrite, lead ferrite, or calcium ferrite, manganese bismuth, and hexagonal crystallized cobalt alloy have been developed as alternatives conventionally used ferromagnetic particles. These particles are very suitable as ferromagnetic particles of a magnetic recording medium for high density recording because they are ferromagnetic hexagonal crystallized tabular shape particles having an axis of easy magnetization in a direction vertical to its flat surface.
Particularly for a video tape, with the increased tendency that recording wavelength is shortened and that width of the recording tracks is narrowed, extremely high density recording has been required. Also, a video tape using ferromagnetic particles (hereinafter referred to as a "barium ferrite, etc.") which are hexagonal crystallized tabular shape particles have an axis of easy magnetization in a direction vertical to their flat surface has come to be used.
When powder of "barium ferrite, etc." is used, it is known that higher density recording can be achieved by smoothing the surface of a magnetic layer, and therefore electromagnetic properties of a magnetic recording medium can be improved.
However, when the surface of a magnetic layer is made smooth, the friction coefficient of contact surface between a magnetic layer and an apparatus system is increased during tape running, whereby the magnetic layer tends to be damaged or even peeled apart in some cases in a short time period. Particularly for a video tape, a magnetic layer is sometimes put under harsh conditions, such as when the magnetic layer is put into a still mode. Therefore, the increase of friction coefficient of a magnetic layer leads to shortened life (still life) of the magnetic layer in the still mode. Accordingly, improvement of running durability of a magnetic layer of a video tape has been desired.
Hitherto, a polyester polyurethane resin has been used as an effective binder to improve wear resistance of a magnetic layer, and further as an improved usage, carbonate polyester polyurethane has been proposed. Binders such as polyvinyl chloride and nitrocellulsoe and the like can be mixed to increase lubricity of the polyurethane. Further, it is proposed that various organic additives such as lauric acid, myristic acid, oleic acid or dispersing agents of esters thereof are used in order to improve dispersibility and surface smoothness. However, in a conventional method, fine powder of "barium ferrite, etc." cannot be dispersed with a binder used in a relatively small amount, and output, dispersibility, and running durability cannot be improved at the same time.